1. Field of the Invention
This invention relates to a novel ultrafine fiber entangled sheet, more particularly, to a novel artificial leather comprising a surface portion of super-entangled fibers having a very high fiber density coefficient and very small amount of a resin. The artificial leather has excellent softness and strength, and is free from rubbery undesirable elasticity. The present invention also relates to a grained artificial leather having a back surface layer which comprises a super-entangled fibers and is preferably substantially free of resin.
2. Description of the Prior Art
Typical examples of conventional non-woven fabrics include (1) non-woven fabric which is produced by needle-punching a web, and (2) non-woven fabric as disclosed in Japanese Patent Publication No. 24699/1969 in which the fiber bundles are entangled with one another while maintaining the bundle form. However, since fabric (1) has a fiber which is relatively thick and has a substantial amount of elastomer, the non-woven fabric is hard and elastic. Hence, the commercial value of this non-woven fabric has been considerably limited. Although fabric (2) is softer than fabric (1), it is easy to break and is still not soft enough. Also, fabric (2) is undesirably elastic and has extremely low shape retention.
U.S. Pat. No. 4,145,468 discloses a fiber sheet comprising a woven or knitted fabric entangled with non-woven fabric by water jet and an artificial leather made thereof. However the artificial leather has rubber-like undesirable elasticity because of a thick surface layer of elastomer and a large amount of impregnated elastomer.
With regard to grained sheets, the grain of conventional synthetic leather consists of a porous or nonporous layer of resin, such as polyurethane elastomer, or of a laminate of a porous layer with a nonporous layer. However, synthetic leather having such a grain has a very undesirable hard rubber-like feel, low crumple resistance, excessively uniform and shallow surface luster, and other disadvantages.
To eliminate these drawbacks, various proposals have been made. These proposals include:
(1) Various fillers, such as fine particles, are added in forming the grain.
(2) Ultrafine fibers are arranged along the surface and combined with a porous material to form the grain. (Japanese Patent Publication No. 40921/1974).
(3) A surface fluff fiber and resin are combined to form the grain.
(4) The surface fibers are melted or dissolved so as to locally bond the fibers and form the grain.
However, method (1) has drawbacks in that the flexibility is reduced and the grain luster of the product is diminished by addition of the fillers. Since the product obtained by method (2) has a grain fiber structure in which the ultrafine fibers are arranged along the surface in bundle form, surface fluffs and peeling develop along the surface of the arrangement of the fiber bundles to cause "loose grain" if the sheet or leather is strongly crumpled or if a shearing stress is repeatedly applied to the sheet. Where the crumpling, or repeated shearing stress continues, cracks eventually occur on the surface. Moreover, fine unevenness occurs on the surface along the bundles of the ultrafine fibers and degrades the surface appearance. The products obtained by methods (3) or (4) have drawbacks in that the surface cracks relatively easily, severely degrading the appearance of the leather, when the sheet is repeatedly bent or a shearing stress is repeatedly applied to the sheet.